This invention relates generally to improvements in control systems. More particularly, it relates to improvements in control systems for maintaining two or more otherwise independent devices in speed synchronism with each other.
In U.S. patent application Ser. No. 217,925, filed on Jan. 14, 1972, by Robert I. White and assigned to the same assignee as is this application, there is disclosed a synchronizing control system which utilizes a pulse resolver to provide an output proportional to the phase relationship of a pulse derived from a master pulse source and a pulse derived from a slave device and representative of the actual speed of the slave device. In that application the particular advantages and utility of such a device in connection with sound motion picture apparatus is disclosed.
It has been found that the performance, and, therefore, the utility of the apparatus disclosed in application Ser. No. 217,925 can be considerably enhanced by the provision of a means which can accommodate to the differences in the time required for a given master device and a given slave device to go from zero to steady state or operating speed. That is to say, that where any given camera or a projector is being synchronized with any given tape recorder or other device, the electrical and mechanical characteristics of the devices so synchronized may be so different that one reaches operating or steady state speed at some time prior or subsequent to this condition being achieved by the other device, and a permanent out of sync condition may then be maintained by the resolver.
Also, due to a temporary film jam a camera slave to a recorder may lose a frame or two, and although there may be apparent speed synchronism there will be no real synchronism between the film and the sound.
Therefore, it is an object of this invention to provide a novel synchronizing system which is capable of recognizing that one device is considerably out of synchronism with another device and to provide a control signal effective to control the slave device in such a way as to insure first the acheivement of synchronism and then the maintenance of synchronism.
It is another object of this invention to provide a novel synchronizing control system wherein a slave device may lead or lag a master by a number of time periods but which provides a memory of the number of pulses lost or gained and corrects for the resulting error.